1. Field of the Invention
This invention relates to a method for producing aluminum titanate in the form of a powdered primary material, ready for making aluminum titanate ceramics, by conventional ceramic techniques. The invention also relates to a method for producing the mixed oxide powder from spent pickle liquor from titanium production by adding aluminum scrap or alumina salts to the same, or equally from aluminum or titanium scrap dissolved in acidic mixture, in both cases by complete recovery of the acids and production of the oxides, which after thermal treatment give the aluminum titanate material.
2. Description of the Prior Art
Aluminum titanate is a chemical component, usually made from aluminum oxide and titanium dioxide powders after intensive mixing by a solid state reaction. It has gained considerable interest for its application in engineering ceramics, especially for motor engine construction material due to its low thermal expansion, as well as high thermal stability, for example to be used as a port liner insulating material. But also its suitability as a refractory material for insulations in ovens, or its application in metal casting or glass melting as crucible material or in form of discharge grooves, has been reported. In general this material is suggested for applications where high resistance to thermal shocks is required.
Aluminum titanate, physically spoken, is a solid solution between Al.sub.2 O.sub.3 and TiO.sub.2 with the formula Al.sub.2 TiO.sub.5 (AL.sub.2 O.sub.3.TiO.sub.2) with the molecular weight 182.1. It is a white powder or after solid forming a white ceramic material.
Production methods by solid state reaction starting from well mixed powders of Al.sub.2 O.sub.3 and TiO.sub.2 are described in patents EP-0036052 (1983), EP-0036462 (1983), EP0036868 (1983), U.S. Pat. No. 2,776,869 (1952), FR-PS No. 1.349,020 (1963) or DDR-PS No. 29.794 (1962). Although it is obviously simple to produce, in fact the reaction kinetics are slow and the product formation from its powdered precursors is reported to proceed at elevated temperatures, over 1600.degree. C., in oxidising atmosphere and very long firing times of ten to twenty hours. Within the temperature range of 800.degree. C. and 1100.degree. C. the reaction is completely reversible, which means that the production of aluminum titanate is immediately followed by its decomposition. The reaction selectivity of this solid state process thus reported seems not to be easily achieved to yield in complete transformation of its precursors.
Further processes, yet scarcely reported for this special product, is the sol-gel route to get the product by precipitation and hydrolysis reactions from the corresponding metal--, i.e. aluminum- and titanium-alcoholate precursors and subsequent calcination to the final product.
Aluminum titanate powder thus formed by one of these processes then can be transferred to the final ceramic form by slip casting, extrusion or cold powder pressing and final sintering. The ceramic has excellent thermal stability up to 1850.degree. C. and outranging thermal shock stability. The final product Al.sub.2 TiO.sub.5 is composed of 56% Al.sub.2 O.sub.3 and 44% TiO.sub.2. It crystallizes orthorhombic, Cmcm space groups, and the industrially one used relates to the .beta.-crystallographic form, also called tialite.